A known seat sliding apparatus for a vehicle is disclosed in JP2005-82059A. As illustrated in FIG. 10, the seat sliding apparatus disclosed includes a lower rail 100, an upper rail 110, a lock mechanism 120, and a release lever 125. The lower rail 100 is fixed to a vehicle floor. The upper rail 110 is fixed to a vehicle seat and movably supported relative to the lower rail 100. The lock mechanism 120 includes multiple lock bores 104a (lock portion) and a lock member 123. The lock bores 104a are provided at the lower rail 100 in a longitudinal direction thereof. The lock member 123 is provided at the upper rail 110 so as to be rotatable on a rotational axis extending in a longitudinal direction of the upper rail 110, and is engageable with and disengageable from the lock bores 104a. 
More specifically, the lower rail 100 includes a base bottom portion 101 arranged substantially in parallel with the vehicle floor, a first side portion 102 upwardly extending from one end of the base bottom portion 101, an upper portion 103 inwardly extending from an upper end of the first side portion 102, and a second side portion 104 downwardly extending from an inner one end of the upper portion 103. The lock bores 104a are provided at the second side portion 104. In addition, the upper rail 110 includes a base top portion 111 arranged substantially in parallel with the base bottom portion 101 of the lower rail 100, a first extending portion 112 downwardly extending from one end of the base top portion 111, a connecting portion 113 outwardly extending from a lower end of the first extending portion 112, and a second extending portion 114 upwardly extending from an outer one end of the connecting portion 113. Further, through-holes 112a and 114a are provided at the first extending portion 112 and the second extending portion 114 of the upper rail 110, respectively, so as to face respective lock bores 104a on both sides of the second side portion 104 of the lower rail 100.
A bracket 130 including a pin 131 at an end is fixed to the base top portion 111 of the upper rail 110. A spring 132 is wound on the pin 131. Because of a function of the spring 132, the lock member 123 is biased in a direction where the upper rail 110 is locked with the lower rail 100. When a link portion 123a, provided as a part of the lock member 123, is pressed by the release lever 125, the lock member 123 is brought to rotate against a biasing force of the spring 132 to thereby release the engagement between the lock bores 104a and the lock member 123. The release lever 125 is configured to be pressed down when an operation lever (not shown) is pulled up.
According to the aforementioned seat sliding apparatus for a vehicle, in the cases where the operation lever is not activated, the release lever 125 is raised or lifted and thus the upper rail 110 and the lower rail 100 are held in the locked state. When the operation lever is pulled up, the release lever 125 is then pulled down to thereby rotate the lock member 123 on the rotational axis. As a result, the upper rail 110 and the lower rail 100 are brought to the unlocked state so that the upper rail 110 becomes movable relative to the lower rail 100.
However, according to the aforementioned seat sliding apparatus, the lock bores 104a are provided at the second side portion 104, which leads to an elongated second side portion 104 of the lower rail 100. In addition, the through-holes 112a and 114a are provided at the first extending portion 112 and the second extending portion 114 of the upper rail 110, respectively, so as to face the respective lock bores 104a. As a result, a difficult or complicated molding and a large cross-sectional area may be inevitable for the aforementioned seat sliding apparatus.
Thus, a need exits for a seat sliding apparatus for a vehicle which is not susceptible to the drawback mentioned above.